This invention relates to optical amplifiers.
A paper by E. Delevaque et al entitled, `Gain Control in Erbium-Doped Fibre Amplifiers by Lasing at 1480 nm with photo induced Bragg Gratings Written on Fibre Ends`, Electronics Letters 10 Jun. 1993, Vol. 29, No. 12, pages 1112-4, describes how the gain afforded by an optical amplifier can be controlled by providing its optically amplifying medium with wavelength selective feedback sufficient to cause it to lase at some predetermined wavelength separated from the waveband within which the amplifier is designed to function as an amplifier.
A consequence of this form of gain control is that the amplified output signal provided by the amplifier is accompanied by laser emission generated by the amplifier.